1. Field of Invention
The present invention relates to an apparatus for digital signal processing, and more specifically, to an apparatus for real time two-dimensional discrete cosine transform (DCT) suitable for implementing into a very large scale integrated (VLSI) circuit.
2. Description of Related Art
In order to implement a number of international video standards, such as Joint Photographic Experts Group (JPEG), Motion Picture Experts Group (MPEG) and H.261, a circuit for fast video data coding or compressing is required. How to increase data transformation efficiency during data coding or compressing has become the most important issue. Since the Discrete Cosine Transform (DCT) process is one of orthogonal transform techniques which have higher transformation efficiency, it has been widely used in video systems for data coding.
Even though efforts have been made to simplify the DCT algorithm, a conventional DCT circuit is still very complicated. In addition, the efficiency that can be obtained from conventional circuits is insufficient to satisfy the requirements of a real time DCT. Conventional circuits are not properly designed to achieve the desired result. For instance, in order to reduce the circuit dimension, methods such as data feedback may be adopted in the circuit design, thus increasing executing time of data transformation. Without skillful arrangement of data flow or timing relationships, operation rates of the DCT circuit will be too low to conform the requirements of the aforementioned international standards.
Furthermore, because multipliers which have very low operating rates are utilized in the conventional DCT circuit, the transformation efficiency of the DCT circuit is affected. Thus, real time operation is difficult to achieve. Though read-only-memory (ROM) devices can take the place of the multipliers of the DCT circuit to increase the efficiency, the ROM devices with very large capacity are required for the 2-D transformation. Therefore, the circuit dimension will be too large to satisfy the requirement of a VLSI circuit.